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Question DetailsAsked on 5/2/2011

We had a Carrier gas furnace and a central AC unit installed in about 2000. The contractor told us that the Honeywell high-density media filter we had was much less efficient than the electrostatic filter he marketed, and because we have pets and allergies we went for it. After the installation we had the ductwork cleaned and we were looking forward to much cleaner air in the house, but that was not to be. We began to notice an accumulation of greyish, lint-like dust throughout the house so we contacted the contractor about the issue. His first fix was to install a small media filter ahead of the electrostatic filter, but it was so loose in the housing we noticed that particulate could get around it unimpeded. When we told him that there was no improvement he suggested that the clothes dryer (located within 5-6 feet of the furnace) was likely leaking lint into the basement and the furnace was picking it up and recirculating it. We dutifully purchased a new washer and dryer and installed new dryer ductwork making sure that every seam was wrapped with silver duct tape. The problem continued. In desperation I asked the contractor to remove the electrostatic filter and replace it with another high-density media filter, and to his credit he did so. When that showed no improvement he reinstalled the electrostatic filter and we are back to square one.

We have had the ductwork cleaned twice since the installation - once conventionally and once by an "eco-friendly" scam that apparently provided their own evidence of what they were removing from our ducts. In 2009 we had all our windows replaced with vinyl sash windows, partly because the old windows were inefficient single pane and also because the sashes leaked badly. Nobody seems to be abe to point us in the right direction and I am ready to pull my hair out.

7 Answers

Do you smoke in the house ? this will leave grey dust like linty stuff on wood surfaces. Do you leave your doors open for a while in the evenings.If not inspect the return's very close to make sure there are no leaks.It sounds like you have a home on a conventional foundation and it is pulling dust from under the house or attic area, also check the unit if it is in the attic to make sure that there are no gaps in the unit itself that could be pulling dust in. Other than that some one will have to just look until it is found. How old is your carpet ? It could be coming apart creating dust.

Your problem is absolutely positively an imbalance in the duct system, most likely on the return side of the system, pulling dirt from the crawlspace, attic or basement; wherever your system is located. Everyone knows the heater and air-conditioner needs to be calculated for the proper size but no one (including some HVAC contractors) recognizes the importance of the duct system. It relates to the pressure produced by the blower section in your heater. Each furnace produces a certain amount of pressure (or Cubic Foot of Air Per Minute) when attached to the existing ductwork. This is not an arbitrary number and must be calculated when installing a new system. Any inconsistencies with the duct-work should have been discussed with you prior to installation. If that contractor knew how to test and evaluate a duct system! The only way to address this problem now is to have a certified NCI contractor come out and perform testing and balancing on the duct-work to stabilize the supply and return C.F.M. into the living space. You can read more if you click on the attached link. You can also check out my YouTube videos of real houses constructed with underperforming ductwork-resulting in poor airflow.

A leak in the return air duct that is pulling outside air into the house.

or

Your duct supply air leaks are greater than the return air leak, and therefore the house is depressurising when the system runs. This is pulling outside air into the house through gaps and cracks in the shell.

Run the system and open an exterior door a small amount, and see which way the air moves across it. Then try closing all the interior doors and do the test again. When a room pressurises because the air cannot return to the ac unit, this can cause a depressurization in the rest of the house as well.

The solution is the same either way: Repair or Replace the duct system. Add transfer grilles to the bedrooms for a return air path or undercut the doors more.

It is too bad that nearly all AC contractors do not take the full system into account, and do a disservice to the properties. I happen to be an energy geek and we deal with this stuff every day.

Below is a link to a blog that I commonly comment on that has lots of postings that cover a lot of this kind of stuff.

I am exactly in the same situation like you. Even in my house we see the same greyish, lint-like dust. It hardly takes 2-3days and within a week we can see a layer of dust on the furniture. I am seeing this problem since the day i bought this house 3years ago. I tried changing the filters frequently, permanent filters, not opening the door or windows at all etc. None of them solved the problem.

Me and and my wife are already tired of cleaning the dust and we are not sure what else we should do. Sometimes i curse myself for buying a 28year old house after seeing this dust problem. We got our duct system cleaned.

The only additional thing i have to mention is i have blown in insulation in my attic. But the heating registers are at ground level. Also, i haven't called any contractor for anual maintenance of the furnace since the past 3years because the heating system is just 4years old.

I hope someone can help me to fix this problem or direct us who should we contact to find the root cause of this problem.

It's the attic blown insulation! wherever your main intake vent is the nearest outflow vent will be the one with a duct leak. That way it blows all over the house and everyone gets to inhale that crap!

I have had the same problem for the past 4 months after living in the same townhouse for 10+ years. No real prior issue. But recently my vaccum has been picking up an abnormal amount of this gray dust, and computers and electronic equipment with fans have been collecting and plugging up with this stuff. And I have been forced to change the gas furance filter every month - using the highest premium available. One night with the lights out I turned on a flashlight to see nothing but solid dust in the air! The light beam from the flashlight was like a solid bar - star wars light saber, as the dust was so thick in the air!!

After thinking about what changed since 4 months prior, I have throughly cleaned the existing carpet, like I do about every year. I am now convinced the carpet backing and the carpet padding are deteriorating, and each further vaccuming is drawing up more of this super fine white/gray dust through the carpet. As in other posts by central AC system experts, I do think I have an in balance in my air flow, drawing in air from the outside. All the same, I swear it is the carpet and padding.

Since I rent, and the landlord it to tight to change the carpet. I rolled out a huge mobile hepa air filter I bought at Brookstone from my old apartment in the new york city. Within an hour the dust was reducing in my bedroom. I am planning to buy a second filter system for the other part of townhouse. I plan to move as soon as possible. And if there are carpets, will be sure they are new before moving in...

Has anyone been able to find the solution to the greyish lint like dust? I have same problem, except only have central heater system, which is never used, so not sure how dust is everywhere if system is not used? Attic is blown insulation so my guess is that is the source, if anyone has a solution it would be great to hear it.